Pitot-Static System Blockage Detector

ABSTRACT

Various implementation described herein are directed to a method for identifying a blockage in a pitot-static system. A pressure signal is received. Pressure fluctuations in the pressure signal are identified. A determination is made as to whether a blockage has occurred in the pitot-static system based on the identified pressure fluctuations.

BACKGROUND

This section is intended to provide background information to facilitatea better understanding of various technologies described herein. As thesection's title implies, this is a discussion of related art. That suchart is related in no way implies that it is prior art. The related artmay or may not be prior art. It should therefore be understood that thestatements in this section are to be read in this light, and not asadmissions of prior art.

Pitot/static systems are used to support airspeed indications and cancause misleading airspeed indications when the pitot tube is blocked byforeign objects or by ice build-up. Normally, the air pressureexperienced by the pitot tube is a total of the outside ambient airpressure (referred to as static pressure) and the dynamic pressure dueto forward flight. A static port is used to measure static pressureindependently, and the measured pressure is subtracted from the totalpressure measured at the pitot tube to provide the resulting dynamicpressure which is then scaled to indicate airspeed. A typical pitot tubeincludes a pressure chamber which often includes a small drain hole toallow accumulated water to exit. If a blockage in the pitot tube occursupstream of a drain hole, the fault is apparent because the air pressurenormally provided by forward flight is first trapped and then leaksthrough the drain until pressure is near equal to the static port. Thisproduces a loss of airspeed indication that is readily apparent.However, in the case of a blockage that includes the drain hole (aswould be the typical case in icing conditions), or a blockage thatoccurs downstream of the drain, the blockage traps the air underpressure in the pitot system holding the airspeed reading at the timethe blockage occurred. When this type of blockage occurs, the conditionis not apparent. Subsequent airspeed changes are not indicatedcorrectly. Furthermore if the altitude increases after blockage occurs,the airspeed indication increases, and if the altitude decreases, theindicated airspeed decreases. These misleading indications can causeconfusion for the flight crew and can lead to inappropriate action. Thiscan also cause a flight control computer or coupled autopilot to go“open loop” if the system autopilot attempts to correct a perceivederror between indicated and target airspeed.

Similarly, a blockage of the static port system is typically notapparent due to the trapped air pressure within the system. In this casethe altitude indication does not change in response to changes inaltitude. Furthermore an increase in altitude will cause a decrease inairspeed reading from the actual airspeed, and a decrease in altitudewill cause an increase in airspeed reading from the actual airspeed.

Traditionally, multiple pitot/static systems are used in large aircraftand automatic comparisons are performed between readings to detect theerrors caused by blockages. Smaller aircraft with a single airspeedindicating system still rely on pilot skill in recognizing a blockedpitot tube or static port condition.

SUMMARY

Described herein are various implementations of a method for identifyinga blockage in a pitot-static system. In one implementation, a pressuresignal is received. Pressure fluctuations in the pressure signal areidentified. A determination is made as to whether a blockage hasoccurred in the pitot-static system based on the identified pressurefluctuations.

In one implementation, the pressure signal may include a total pressuresignal received from a total pressure sensor. The total pressure sensormay be coupled to a pitot tube of the pitot-static system. A predefinedairspeed may be attained prior to receiving the pressure signal.

In one implementation, the pressure signal may include a static pressuresignal. The static pressure signal may be received from a staticpressure sensor. The static pressure sensor may be coupled to a staticport of the pitot-static system. A predefined flight range of a rotorspeed may be attained prior to receiving the pressure signal.

The identified pressure fluctuations may include a noise component. Inone implementation, the noise component may be a rotor blade passagefrequency. In another implementation, the noise component may be alongitudinal vibration frequency.

In one implementation, the identified pressure fluctuations may beisolated to identify pressure fluctuations characteristic of an openport.

In one implementation, the determination of whether the blockage hasoccurred may be processed in a frequency domain.

In one implementation, the determination of whether the blockage hasoccurred may be processed in a time domain.

In one implementation, the blockage may be indicated based on athreshold.

Described herein is an apparatus for identifying a blockage in apitot-static system. In one implementation, the apparatus includes adevice configured to: receive a pressure signal; identify pressurefluctuations in the pressure signal; and determine whether a blockagehas occurred in the pitot-static system based on the identified pressurefluctuations.

In one implementation, the device receives the pressure signal from apressure sensor of the pitot-static system coupled to the device. Thepressure sensor coupled to the device may be a total pressure sensor.The pressure sensor coupled to the device may be a static pressuresensor.

Described herein is a blockage detector for identifying a blockage in apitot-static system. In one implementation, the blockage detectorincludes a pressure sensor. The blockage detector further includes acircuit that: receives a pressure signal from the pressure sensor;identifies pressure fluctuations in the pressure signal; and determineswhether a blockage has occurred in the pitot-static system based on theidentified pressure fluctuations.

The above referenced summary section is provided to introduce aselection of concepts in a simplified form that are further describedbelow in the detailed description section. Additional concepts andvarious other implementations are also described in the detaileddescription. The summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter, nor is itintended to limit the number of inventions described herein.Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of various techniques will hereafter be described withreference to the accompanying drawings. It should be understood,however, that the accompanying drawings illustrate only the variousimplementations described herein and are not meant to limit the scope ofvarious techniques described herein.

FIG. 1 illustrates a rotorcraft in accordance with implementations ofvarious techniques described herein.

FIG. 2 illustrates an example of a pitot-static system in accordancewith implementations of various techniques described herein.

FIG. 3 illustrates an example of a pitot-static system in accordancewith implementations of various techniques described herein.

FIG. 4 illustrates an analog implementation of a blockage detectorcircuit in accordance with implementations of various techniquesdescribed herein.

FIG. 5 illustrates a diagram of a method for identifying a blockage in apitot-static system in accordance with implementations of varioustechniques described herein.

FIG. 6 illustrates a computing system in accordance with implementationsof various techniques described herein.

DETAILED DESCRIPTION

Rotorcraft have specific characteristics that normally presentchallenges related to providing stable airspeed indication. At lowspeed, rotor wash creates variations in pressure that occur as eachblade passes the pitot and static system. This creates pressure pulsesat each port at or near the blade passage frequency. At higher speeds,where rotor wash moves rearward away from the pitot tube, the airframeremains subject to longitudinal vibration. This longitudinal vibrationis primarily made up of multitudes of the main rotor frequencies. Thevariations in pressure and the longitudinal vibration translate intonuisance noise in the airspeed system. This nuisance noise is typicallyfiltered and removed in order to provide stable air data parameters thatare suitable for presentation on flight displays to the pilot and foruse by flight control systems. The nuisance signals related torotorcraft dynamics can be utilized as a way to detect that the pitottube and static port are open to the outside atmosphere and are notblocked. If a pitot tube or static port were to become blocked, e.g., byice or a foreign object, the pressure value detected becomes a clean andrelatively constant signal, possibly slowly changing due toequalization, but devoid of the nuisance characteristics typical ofhelicopter air data systems.

Implementations of the present disclosure monitor the total pressurevalue or the static pressure value at a point in the system prior to theapplication of low-pass filtering to remove the nuisancecharacteristics. Typically Air Data Computers (ADCs) provide minimalfiltering so that down-stream systems such as flight display systems andflight control computers can provide parameter filtering specific totheir needs. As such, implementations of the present disclosure may beincluded in a variety of hosting systems coupled either pneumatically orelectrically to air data signals typically available in a rotorcraft. Inorder to determine a pitot tube blockage, the total pressure value maybe determined using air data computer, a stand-alone pressure detectorcircuit, or similar devices. Total pressure is the air pressureexperienced by the pitot tube without the effects of the static pressureremoved. The total pressure signal is then either high-pass or notchfiltered in order to remove the basic pressure data and retain only the“nuisance noise components” that include rotor wash and longitudinalvibration frequencies. If the resulting signal exceeds a threshold thatindicates the minimum noise component signal for a normal open pitottube, the pitot tube is determined to be operating normally. If thenoise component is below a threshold, then the system is determined tobe blocked and the blockage is indicated to the pilot via a displaysystem or indicator. In one implementation, the detection system may beactivated upon reaching a minimum airspeed and/or a minimum rotorrevolutions per minute (RPM) reading. The threshold for the noisecomponent may be tailored as a function of the indicated airspeed and assuch, provides an ability to refine the threshold as necessary.

Implementations for determining static port blockage operate similarly,however, the effect of multi-port systems is also considered. Staticsystems often include two cross-connected ports in each systemspecifically intended to reduce errors caused by sideways flight andalso to significantly reduce the effects of rotor-wash at low speed. Asingle port blockage has the effect of increasing the nuisancecomponents, while a total blockage causes the relatively clean signalsimilar to a blocked pitot. Therefore a range of a noise componentsignal as a function of airspeed, isolated by high-pass or notchfiltering will indicate a properly operating static port system. Aresulting signal below a specific threshold indicates a blocked system,but a signal above a threshold may be used to indicate a developing orpartial blockage. For static port detection systems a mechanism may beincluded to prevent false alarms for when the aircraft is stationaryprior to rotors turning, i.e., when the nuisance noise component is notpresent. Minimum airspeed and/or rotor RPM are parameters that can beused to prevent false alarms. Implementations of the present disclosurecan be: included within a traditional air data computer or similardevices; built into systems that monitor total pressure and staticpressure reported by an air data computer or similar devices, such asflight control systems, flight display systems, or ancillaryaccessories; or built into dedicated equipment monitoring the pneumatictubing associated with a pitot or static system.

FIG. 1 illustrates a rotorcraft 100 according to one implementation.Rotorcraft 100 has a rotor system 103 with a plurality of main rotorblades 111. Rotorcraft 100 further includes a fuselage 105, landing gear107, a tail member 109, and tail rotor blades 113. An engine (not shown)supplies torque to a main rotor mast 117 to rotate main rotor blades111. The engine also supplies torque to a tail rotor drive shaft (notshown) to rotate tail rotor blades 113. The pitch of each main rotorblade 111 can be selectively controlled in order to selectively controldirection, thrust, and lift of rotorcraft 100. Further, the pitch oftail rotor blades 113 can be selectively controlled in order toselectively control yaw of rotorcraft 100.

Rotorcraft 100 includes one or more pitot tubes 119, 121. Rotorcraft 100also includes one or more static pressure ports 123, 125, 127, 129 on aleft side (left static pressure ports 123, 125) and a right side (rightstatic pressure ports 127, 129) of rotorcraft 100.

Pitot tubes 119, 121 and static pressure ports 123, 125, 127, 129 may bepart of a pitot-static system. The pitot-static system may include asystem of pressure-sensitive instruments that is most often used inaviation to determine an airspeed, altitude, and altitude trend ofrotorcraft 100. A pitot-static system generally includes at least onepitot tube, at least one static port. Other elements that may beconnected are air data computers, flight data recorders, altitudeencoders, cabin pressurization controllers, and various accessories.

Rotorcraft 100 is illustrated for exemplary purposes. It should beappreciated that implementations of the present disclosure may be usedon aircraft other than rotorcraft, e.g., airplanes, tilt rotors, orunmanned aircraft. Further, implementations of the present disclosuremay be used on non-aircraft vehicles.

FIG. 2 illustrates an example of a pitot-static system 200. Pitot-staticsystem 200 may include pitot tube 205, static pressure ports 207, 209,pneumatic lines 213, 215 and an air data computer (ADC) 223. Pitot tube205 may include a pitot orifice, a pressure chamber, a drain hole andheater (HTR). Pressure readings can be determined from relative windentering the pressure chamber through the pitot orifice.

A total pressure line 213 couples the pitot tube 205 to total pressuresensor 217 of ADC 223. A static pressure line 215 couples the staticpressure ports 207, 209 to static pressure sensor 219 of ADC 223. An airtemperature reading may be provided from temperature element 211 totemperature sensor 221 of ADC 223. ADC 223 includes a processor 225 thatreceives input from various sensors (e.g., sensors 217, 219, 221) anddetermines various ADC parameters. The ADC 223 may provide the variousADC parameters to various aircraft systems using data transfer ports227, 229, 231.

In one implementation, the data transfer ports may be Aeronautical RadioInc. (ARINC) 429 standard ports. ARINC 429 is a data transfer standardfor aircraft avionics. ARINC 429 uses a self-clocking,self-synchronizing data bus protocol (transmit and receive are onseparate ports). The physical connection wires for each port are twistedpairs carrying balanced differential signaling. The ADC parameters mayinclude: calibrated airspeed, true airspeed, corrected altitude,pressure altitude, density altitude, vertical speed, static airtemperature, total pressure, dynamic pressure, static pressure, Machnumber, and angle of attack. The various user aircraft systems mayinclude: flight displays, flight control systems, and flight navigationsystems.

Pitot static system 200 may use a second type of ADC (ADC 243) that isconfigured to work with a dynamic pressure sensor (dynamic pressuresensor 237). In this implementation, a total pressure line 233 couplesthe pitot tube 205 to dynamic pressure sensor 237 of ADC 243. A staticpressure line 235 couples the static pressure ports 207, 209 to staticpressure sensor 239 of ADC 243. Pressure data from the dynamic sensorcan be converted to total pressure data by ADC 243 using static pressuredata from static pressure sensor 239. An air temperature reading may beprovided from temperature element 211 to temperature sensor 241 of ADC243. ADC 243 includes a processor 245 that receives input from varioussensors (e.g., sensors 237, 239, 241) and determines various ADCparameters. Processor 245 may also receive data from miscellaneousinput/sensor 247 and angle of attack (AOA) data from AOA sensor 255. TheADC 243 may provide the various ADC parameters to various aircraftsystems using data transfer ports 249, 251, 253.

ADC 243 can be used to detect a pitot tube blockage and/or a static portblockage. Although implementations described herein refer to ADC 243,other systems can be used to determine pitot tube and static portblockages. Processing for blockage detection can also be performed insystems that have access to air data computer digital outputs, e.g., viaa separate blockage detector 257 implemented in a display system,automatic flight control system, navigation system, or a dedicatedsystem monitoring the digital data.

ADC 243 uses the “total pressure” parameter to monitor for pitotblockages. In one implementation, prior to initiation of pitot tubeblockage monitoring, a minimum airspeed should be attained. In oneimplementation, pitot tube monitoring is initiated when the airspeed isgreater than or equal to 30 knots.

ADC 243 uses the “static pressure” parameter to monitor for static portblockages. In one implementation, prior to initiation of static portblockage monitoring, a rotor speed should be within a flight range.

Noise components of the total pressure and/or static pressure parametersmay be calculated by the ADC 223, 243. These noise components mayinclude a rotor blade passage frequency and a longitudinal vibrationfrequency. When the noise components exceed a threshold that indicates anormal open pitot tube, the system is determined to be operatingnormally. When the noise component is below a threshold, then the systemis determined to be blocked and an indication of the blockage isprovided to the pilot via a display system or other audio and/or visualindicator.

In one implementation, blockage detection for pitot tubes and staticports may be processed in the frequency domain. The parameter data(e.g., total pressure and/or static pressure) can be high-pass filteredor notch filtered to isolate the frequency range of interest. Theisolated frequency range of interest may be applied to noise componentsof the total pressure and/or static pressure data. These noisecomponents may include rotor blade passage frequency and longitudinalvibration frequency.

A mean amplitude of the resulting output (e.g., the noise components) ofthe high-pass filter or notch filter may be detected and provided asoutput. If the output is above a threshold, the blockage detectorindicates that the pneumatic line is not blocked and is workingnormally. If the output of the high-pass filter or notch filter remainsbelow the threshold for a period of time, the pneumatic line isconsidered blocked. In one implementation, the threshold is determinedby a flight test. In one implementation, the period of time used todetermine whether a blockage has occurred is approximately 2 to 3seconds.

In one implementation, blockage detection for pitot tubes and staticports may be processed in the time domain. A series of samples of thepressure (total pressure and/or static pressure) data corresponding toat least two rotor blade passages can be periodically captured. Adifference between the maximum value and minimum value sample in thecaptured data can be determined. If the difference is above a threshold,the blockage detector indicates the pneumatic line is not blocked. Ifthe difference is below a threshold, then the blockage detectorindicates the pneumatic line is potentially blocked. In oneimplementation, the threshold can be determined by a flight test. In oneimplementation, the threshold may vary as a function of altitude.

In one implementation, after a predefined number of these samples/checksin sequence indicating a potential blockage in the pitot tube and/orstatic port, the blockage detection system will indicate a blockage. Inone implementation, once a blockage is indicated, a predefined number ofthese samples/checks indicating that the pitot tube and/or static portis not blocked would cause the system to indicate no blockage.

Pitot static system 200 may be used to detect a blockage in pitot tube205 and/or static ports 207, 209 using a standalone circuit. FIG. 3illustrates an example of a pitot static system using a standalonecircuit (e.g., blockage detector 300, 305) to detect a blockage in pitottube 205 and/or static pressure ports 207, 209. Blockage detector 300 isincorporated as a dedicated blockage detector coupled to total pressureline 213, 233. Blockage detector 305 is incorporated as a dedicatedblockage detector coupled to static pressure line 215, 235. Blockagedetector 300, 305 may be configured to work with ADC 223, 243 or withtraditional pneumatic instruments. Each blockage detector 300, 305includes a blockage detector circuit 321, 329 and a pressure sensorcoupled to a respective pressure line 213, 215, 233, 235. The blockagedetector 300, 305 receives pressure readings from sensor 319, 327. Thecircuit 321, 329 determines whether a blockage has occurred based on anoise component of the received pressure readings. When the circuit 321,329 determines that a blockage has occurred, circuit 321, 329 providesan indication of the blockage to the pilot via indicator 317, 325.Indicator 317, 325 may be provided via a display system or some otheraudio and/or visual indicator.

FIG. 4 illustrates an analog implementation of a blockage detectorcircuit, e.g., blockage detector circuit 321, 329. In thisimplementation, pressure sensor 319, 327 of blockage detector circuit321, 329 is coupled to pneumatic line 213, 215. Pressure sensor 319, 327is coupled to circuit 321, 329. When a blockage is detected by circuit321, 329, an indication is provided to indicator 317, 325. Circuit 321,329 includes a frequency notch filter 402, amplitude detector 404,threshold comparator 406 and a monostable timer 408.

Notch filter 402 can be tuned to pass signals in a frequency range thatincludes rotor blade frequency and major in-flight longitudinalvibration frequencies. Amplitude detector 404 converts the result of thenotch filter 402 to a DC signal proportional to the amplitude of theoscillations within the frequency of interest. Threshold comparator 406determines whether the signal amplitude meets the minimum criteria (REF)to establish that the port to the pneumatic line is open. If the minimumcriteria is met, threshold comparator 406 applies a signal that preventsthe monostable timer from indicating a blockage. If the signal dropsbelow the threshold (e.g., the minimum criteria) and remains there for aperiod of time determined by the timer 408, the timer activates thewarning indicator 317, 325.

In one implementation, the enable signal (ENABLE) is used to preventfalse blockage alerts when the helicopter rotors are not turning or theaircraft is not in forward flight. The enable signal (ENABLE) may bebased on airspeed in the case of a pitot blockage monitor/detector. Theenable signal may be based on rotor speed in the case of a static portblockage monitor/detector.

FIG. 5 illustrates a block diagram of a method for identifying ablockage in a pitot-static system. At block 505 a pressure signal isreceived. The pressure signal may be received by, for example ADC 243 orany other system having a blockage detector, e.g., blockage detector257, 300, 305, capable of processing a pressure signal to identify ablockage.

In one implementation, the pressure signal is a total pressuresignal/parameter that is used to monitor for pitot blockages. In oneimplementation, prior to initiation of pitot tube blockage monitoring, aminimum or predefined airspeed should be attained. In oneimplementation, pitot tube monitoring is initiated when the airspeed isgreater than or equal to 30 knots.

In one implementation, the pressure signal is a static pressuresignal/parameter that is used to monitor for static port blockages. Inone implementation, prior to initiation of static port blockagemonitoring, a rotor speed should be within a predefined flight range.

At block 510, pressure fluctuations are identified in the pressuresignal. In one implementation, the pressure fluctuations may be noisecomponents, oscillation components and/or transient components. Noisecomponents of the total pressure and/or static pressure parameters maybe determined by the ADC 223, 243. These noise components may include arotor blade passage frequency and a longitudinal vibration frequency.

At block 515, a determination is made as to whether a blockage hasoccurred based on the identified pressure fluctuations. When thepressure fluctuations exceed a threshold that indicates a normal openpitot tube or static port, the system is determined to be operatingnormally. When the pressure fluctuation is below a threshold, the systemis determined to be blocked and an indication of the blockage isprovided to the pilot via a display system or other audio and/or visualindicator.

In one implementation, blockage detection for pitot tubes and staticports may be processed in the frequency domain. The parameter data(e.g., total pressure and/or static pressure) can be high-pass filteredor notch filtered to isolate the frequency range of interest. Theisolated frequency range of interest may be applied to determinepressure fluctuations of the total pressure and/or static pressure data.These pressure fluctuations may include rotor blade passage frequencyand longitudinal vibration frequency.

A mean amplitude of the resulting output (e.g., the pressurefluctuations) of the high-pass filter or notch filter may be detectedand provided as output. If the output is above a threshold, the blockagedetector indicates that the pneumatic line is not blocked and is workingnormally. If the output of the high-pass filter or notch filter remainsbelow the threshold for a period of time, the pneumatic line isconsidered blocked. In one implementation, the threshold is determinedby a flight test. In one implementation, the period of time used todetermine whether a blockage has occurred is approximately 2 to 3seconds.

In one implementation, blockage detection for pitot tubes and staticports may be processed in the time domain. A series of samples of thepressure (total pressure and/or static pressure) data corresponding toat least two rotor blade passages can be periodically captured. Adifference between the maximum value and minimum value sample in thecaptured data can be determined. If the difference is above a thresholdthe blockage detector indicates that the pneumatic line is not blocked.If the difference is below a threshold then the pneumatic line ispotentially blocked. In one implementation, the threshold can bedetermined by a flight test. In one implementation, the threshold mayvary as a function of altitude.

In one implementation, after a predefined number of these samples/checksin sequence indicating a potential blockage in the pitot tube and/orstatic port, the blockage detection system will indicate a blockage. Inone implementation, once a blockage is indicated, a predefined number ofthese samples/checks indicating that the pitot tube and/or static portis not blocked would cause the system to indicate no blockage.

FIG. 6 is a block diagram of a hardware configuration 600 operable toidentify a blockage in a pitot-static system. The hardware configuration600 can include a processor 610, a memory 620, a storage device 630, andan input/output device 640. Each of the components 610, 620, 630, and640 can, for example, be interconnected using a system bus 650. Theprocessor 610 can be capable of processing instructions for executionwithin the hardware configuration 600. In one implementation, theprocessor 610 can be a single-threaded processor. In anotherimplementation, the processor 610 can be a multi-threaded processor. Theprocessor 610 can be capable of processing instructions stored in thememory 620 or on the storage device 630.

The memory 620 can store information within the hardware configuration600. In one implementation, the memory 620 can be a computer-readablemedium. In one implementation, the memory 620 can be a volatile memoryunit. In another implementation, the memory 620 can be a non-volatilememory unit.

In some implementations, the storage device 630 can be capable ofproviding mass storage for the hardware configuration 600. In oneimplementation, the storage device 630 can be a computer-readablemedium. In various different implementations, the storage device 630can, for example, include a hard disk device/drive, an optical diskdevice, flash memory or some other large capacity storage device. Inother implementations, the storage device 630 can be a device externalto the hardware configuration 600.

The input/output device 640 provides input/output operations for thehardware configuration 600. In one implementation, the input/outputdevice 640 can include one or more pitot-static system interfaces,sensors and/or data transfer ports.

The subject matter of this disclosure, and components thereof, can berealized by instructions that upon execution cause one or moreprocessing devices to carry out the processes and functions describedabove. Such instructions can, for example, comprise interpretedinstructions, such as script instructions, e.g., JavaScript orECMAScript instructions, or executable code, or other instructionsstored in a computer readable medium.

Implementations of the subject matter and the functional operationsdescribed in this specification can be provided in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this specification and their structuralequivalents, or in combinations of one or more of them. Embodiments ofthe subject matter described in this specification can be implemented asone or more computer program products, i.e., one or more modules ofcomputer program instructions encoded on a tangible program carrier forexecution by, or to control the operation of, data processing apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program does notnecessarily correspond to a file in a file system. A program can bestored in a portion of a file that holds other programs or data (e.g.,one or more scripts stored in a markup language document), in a singlefile dedicated to the program in question, or in multiple coordinatedfiles (e.g., files that store one or more modules, sub programs, orportions of code). A computer program can be deployed to be executed onone computer or on multiple computers that are located at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

The processes and logic flows described in this specification areperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output thereby tying the process to a particular machine(e.g., a machine programmed to perform the processes described herein).The processes and logic flows can also be performed by, and apparatuscan also be implemented as, special purpose logic circuitry, e.g., anFPGA (field programmable gate array) or an ASIC (application specificintegrated circuit).

Computer readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices (e.g., EPROM, EEPROM, and flash memory devices); magnetic disks(e.g., internal hard disks or removable disks); magneto optical disks;and CD ROM and DVD ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

The discussion above is directed to certain specific implementations. Itis to be understood that the discussion above is only for the purpose ofenabling a person with ordinary skill in the art to make and use anysubject matter defined now or later by the patent “claims” found in anyissued patent herein.

It is specifically intended that the claimed invention not be limited tothe implementations and illustrations contained herein, but includemodified forms of those implementations including portions of theimplementations and combinations of elements of differentimplementations as come within the scope of the following claims. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions may be made to achieve the developers'specific goals, such as compliance with system-related and businessrelated constraints, which may vary from one implementation to another.Moreover, it should be appreciated that such a development effort mightbe complex and time consuming, but would nevertheless be a routineundertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure. Nothing in thisapplication is considered critical or essential to the claimed inventionunless explicitly indicated as being “critical” or “essential.”

In the above detailed description, numerous specific details were setforth in order to provide a thorough understanding of the presentdisclosure. However, it will be apparent to one of ordinary skill in theart that the present disclosure may be practiced without these specificdetails. In other instances, well-known methods, procedures, components,circuits and networks have not been described in detail so as not tounnecessarily obscure aspects of the embodiments.

It will also be understood that, although the terms first, second, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first object or step could betermed a second object or step, and, similarly, a second object or stepcould be termed a first object or step, without departing from the scopeof the invention. The first object or step, and the second object orstep, are both objects or steps, respectively, but they are not to beconsidered the same object or step.

The terminology used in the description of the present disclosure hereinis for the purpose of describing particular implementations only and isnot intended to be limiting of the present disclosure. As used in thedescription of the present disclosure and the appended claims, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items. It will be further understood that the terms“includes,” “including,” “comprises” and/or “comprising,” when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components and/or groups thereof.

As used herein, the term “if” may be construed to mean “when” or “upon”or “in response to determining” or “in response to detecting,” dependingon the context. Similarly, the phrase “if it is determined” or “if [astated condition or event] is detected” may be construed to mean “upondetermining” or “in response to determining” or “upon detecting [thestated condition or event]” or “in response to detecting [the statedcondition or event],” depending on the context. As used herein, theterms “up” and “down”; “upper” and “lower”; “upwardly” and downwardly”;“below” and “above”; and other similar terms indicating relativepositions above or below a given point or element may be used inconnection with some implementations of various technologies describedherein.

While the foregoing is directed to implementations of various techniquesdescribed herein, other and further implementations may be devisedwithout departing from the basic scope thereof, which may be determinedby the claims that follow. Although the subject matter has beendescribed in language specific to structural features and/ormethodological acts, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed as example forms of implementingthe claims.

What is claimed is:
 1. A method for identifying a blockage in apitot-static system, comprising: receiving a pressure signal;identifying pressure fluctuations in the pressure signal; anddetermining whether a blockage has occurred in the pitot-static systembased on the identified pressure fluctuations.
 2. The method of claim 1,wherein the pressure signal comprises a total pressure signal receivedfrom a total pressure sensor.
 3. The method of claim 2, wherein thetotal pressure sensor is coupled to a pitot tube of the pitot-staticsystem.
 4. The method of claim 3, wherein a predefined airspeed isattained prior to receiving the pressure signal.
 5. The method of claim1, wherein the pressure signal comprises a static pressure signal. 6.The method of claim 5, wherein the static pressure signal is receivedfrom a static pressure sensor.
 7. The method of claim 6, wherein thestatic pressure sensor is coupled to a static port of the pitot-staticsystem.
 8. The method of claim 7, wherein a predefined flight range of arotor speed is attained prior to receiving the pressure signal.
 9. Themethod of claim 1, wherein the identified pressure fluctuations comprisea noise component.
 10. The method of claim 9, wherein the noisecomponent comprises a rotor blade passage frequency.
 11. The method ofclaim 9, wherein the noise component comprises a longitudinal vibrationfrequency.
 12. The method of claim 1, further comprising isolating theidentified pressure fluctuations to identify pressure fluctuationscharacteristic of an open port.
 13. The method of claim 1, wherein thedetermination of whether the blockage has occurred is processed in afrequency domain.
 14. The method of claim 1, wherein the determinationof whether the blockage has occurred is processed in a time domain. 15.The method of claim 1, wherein the blockage is indicated based on athreshold.
 16. An apparatus for identifying a blockage in a pitot-staticsystem, comprising: a device configured to: receive a pressure signal;identify pressure fluctuations in the pressure signal; and determinewhether a blockage has occurred in the pitot-static system based on theidentified pressure fluctuations.
 17. The apparatus of claim 16, whereinthe device receives the pressure signal from a pressure sensor of thepitot-static system coupled to the device.
 18. The apparatus of claim17, wherein the pressure sensor coupled to the device comprises a totalpressure sensor.
 19. The apparatus of claim 18, wherein the pressuresensor coupled to the device comprises a static pressure sensor.
 20. Ablockage detector for identifying a blockage in a pitot-static system,comprising: a pressure sensor; and a circuit that: receives a pressuresignal from the pressure sensor; identifies pressure fluctuations in thepressure signal; and determines whether a blockage has occurred in thepitot-static system based on the identified pressure fluctuations.